Method and apparatus for aggregating carriers in wireless communication systems

ABSTRACT

The present invention relates to a method and apparatus for aggregating carriers in wireless communication systems. In the method, a first carrier is set up, and a second carrier is added in addition to the first carrier. In addition, the first carrier is a time division duplex (TDD) carrier for which an uplink subframe and a downlink subframe are positioned at different times in a frame, and the second carrier is a carrier only for a downlink that consists of downlink subframes.

This application is a National Stage Application of International PatentApplication No. PCT/KR2013/002887, filed on Apr. 5, 2013, and claims thebenefit of U.S. Provisional Application Nos. 61/620,449, filed on Apr.5, 2012, 61/636,740, filed on Apr. 23, 2012, 61/667,947, filed on Jul.4, 2012, 61/702,214, filed on Sep. 17, 2012, 61/738,401, filed on Dec.18, 2012 and 61/750,316, filed on Jan. 3, 2013, in the United StatesPatent and Trademark Office, all of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for aggregating carriers in awireless communication system.

2. Related Art

A carrier aggregation system has recently drawn attention. The carrieraggregation system implies a system that configures a broadband byaggregating one or more component carriers (CCs) having a bandwidthsmaller than that of a target broadband when the wireless communicationsystem intends to support the broadband. In the carrier aggregationsystem, a term, serving cell, is also used instead of the CC. Herein,the serving cell consists of a pair of downlink component carrier (DLCC) and uplink component carrier (UL CC), or consists of only the DL CC.That is, the carrier aggregation system is a system in which a pluralityof serving cells is assigned to one user equipment.

Conventionally, in the carrier aggregation system, it is considered toaggregate only CC of the same mode. That is, it is considered toaggregate the CCs that operate in the frequency division duplex (FDD)mode or to aggregate the CCs that operate in the time division duplex(TDD) mode. Particularly, in case of the TDD, it is assumed that the CCswhich are aggregated use the same uplink-downlink (UL-DL) configuration.The UL-DL configuration is to notify which one is used either uplink(UL) or downlink (DL) for the respective subframes within the frame thatis made up of multiple subframes.

However, in the future wireless communication system, it may not berequired to confine the above considerations.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for aggregatingcarriers in a wireless communication system.

In an aspect, a method for aggregating carriers in a wirelesscommunication system includes configuring a first carrier; andconfiguring a second carrier in addition to the first carrier, whereinthe first carrier is a time division duplex (TDD) carrier in whichuplink subframe and downlink subframe are located on different time in aframe, and wherein the second carrier is a downlink only carriercomprised of downlink subframe only.

In another aspect, an apparatus for aggregating carriers in a wirelesscommunication system includes a radio frequency (RF) unit that transmitsand receives a radio signal; and a processor operating functionallyconnected with the RF unit, wherein the process is configured toperform, configuring a first carrier; and configuring a second carrierin addition to the first carrier, wherein the first carrier is a timedivision duplex (TDD) carrier in which uplink subframe and downlinksubframe are located on different time in a frame, and wherein thesecond carrier is a downlink only carrier comprised of downlink subframeonly.

Even in case of introducing a carrier of new type that does not havebackward compatibility with the existing carriers defined in a wirelesscommunication system, it is available to perform carrier aggregationeffectively. In addition, the HARQ-timing according to the carrieraggregation can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of an FDD radio frame.

FIG. 2 shows a structure of a TDD radio frame.

FIG. 3 shows an example of a resource grid for one DL slot.

FIG. 4 shows a structure of a DL subframe.

FIG. 5 shows a structure of a UL subframe.

FIG. 6 shows a frame structure for synchronization signal transmissionin the conventional FDD frame.

FIG. 7 shows a case where two sequences in a logical domain areinterleaved and mapped in a physical domain.

FIG. 8 shows a frame structure for transmitting a synchronization signalin the conventional TDD frame.

FIG. 9 shows an example of comparing a single-carrier system and acarrier aggregation system.

FIG. 10 exemplifies the DL only carrier.

FIG. 11 shows another example of configuring the DL only carrier.

FIG. 12 exemplifies the UL only carrier.

FIG. 13 shows the HARQ-ACK timing in case that Method 1 and Method 4 arecombined.

FIG. 14 is a block diagram showing a wireless apparatus for implementingan embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A user equipment (UE) may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a mobile terminal(MT), a user terminal (UT), a subscriber station (SS), a wirelessdevice, a personal digital assistant (PDA), a wireless modem, a handhelddevice, etc.

A base station (BS) is generally a fixed station that communicates withthe UE and may be referred to as another terminology, such as an evolvednode-B (eNB), a base transceiver system (BTS), an access point, etc.

A communication from the BS to the UE is called a downlink (DL), and acommunication from the UE to the BS is called an uplink (UL). A wirelesscommunication system including the BS and the UE may be a time divisionduplex (TDD) system or a frequency division duplex (FDD) system. The TDDsystem is a wireless communication system for performing UL and DLtransmission/reception by using different times at the same frequencyband. The FDD system is a wireless communication system capable ofsimultaneously performing UL and DL transmission/reception by usingdifferent frequency bands. The wireless communication system can performcommunication by using a radio frame.

FIG. 1 shows a structure of an FDD radio frame.

The FDD radio frame (hereinafter, simply referred to as FDD frame)includes 10 subframes. One subframe includes two consecutive slots.Slots included in the FDD frame are indexed from 0 to 19. The time whichis required to transmit one subframe is defined as transmission timeinterval (TTI) and the TTI may be a minimum scheduling unit. Forexample, one subframe may have a length of 1 millisecond (ms), and oneslot may have a length of 0.5 ms. Assuming that the length of a wirelessframe is T_(f), T_(f)=307200 Ts=10 ms (milli-second).

FIG. 2 shows a structure of a TDD radio frame.

Referring to FIG. 2, the TDD radio frame (hereinafter, TDD frame)includes 10 subframes. The TDD frame includes an uplink (UL) subframe, adownlink (DL) subframe and a specific subframe (S subframe). Whensubframes of the TDD frame are indexed starting from 0, a subframehaving an index #1 and an index #6 may be a special subframe, and thespecial subframe includes a downlink pilot time slot (DwPTS), a guardperiod (GP), and an uplink pilot time slot (UpPTS). The DwPTS is used ina UE for initial cell search, synchronization, or channel estimation.The UpPTS is used in a BS for channel estimation and uplink transmissionsynchronization of the UE. The GP is a period for removing interferencewhich occurs in an uplink due to a multi-path delay of a downlink signalbetween uplink and downlink. The GP and the UpPTS take a role of a timegap.

In the TDD frame, a downlink (DL) subframe and an uplink (UL) subframecoexist. Table 1 below shows an example of a UL-DL configuration of aradio frame.

TABLE 1 Uplink-downlink Downlink-to-Uplink Subframe number configurationSwitch-point periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D

In Table 1, ‘D’ represents a DL subframe, ‘U’ represents a UL subframe,‘S’ represents a special subframe. If receiving the UL-DL configuration,the UE may be aware whether each of the subframes in the TDD subframe isa DL subframe (or S subframe) or a UL subframe.

FIG. 3 shows an example of a resource grid for one DL slot.

Referring to FIG. 3, the DL slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in a time domain, andincludes N_(RB) resource blocks (RBs) in a frequency domain. The RB is aresource allocation unit, and includes one slot in the time domain andincludes a plurality of sequential subcarriers in the frequency domain.The number N_(RB) of RBs included in the DL slot depends on a DLtransmission bandwidth configured in a cell. For example, in the LTEsystem, N_(RB) may be one in the range of 6 to 110. A structure of a ULslot may be the same as the aforementioned structure of the DL slot.

Each element on the resource grid is referred to as a resource element(RE). The RE on the resource grid can be identified by an index pair (k,l) within the slot. Herein, k(k=0, . . . , N_(RB)×12−l) denotes asubcarrier index in the frequency domain, and l(l=0, . . . , 6) denotesan OFDM symbol index in the time domain.

Although it is described in FIG. 3 that one resource block includes 7×12REs consisting of 7 OFDM symbols in the time domain and 12 subcarriersin the frequency domain for example, the number of OFDM symbols and thenumber of subcarriers in the resource block are not limited thereto. Thenumber of OFDM symbols and the number of subcarriers may changevariously depending on a cyclic prefix (CP) length, a frequency spacing,etc. For example, if the CP length corresponds to an extended CP, theresource block includes 6 OFDM symbols. The number of subcarriers in oneOFDM symbol may be selected from 128, 256, 512, 1024, 1536, and 2048.

FIG. 4 shows a structure of a DL subframe.

Referring to FIG. 4, the DL subframe is divided into a control regionand a data region in the time domain. The control region includes up tothree (optionally, up to four) preceding OFDM symbols of a first slot inthe subframe. However, the number of OFDM symbols included in thecontrol region may vary. A physical downlink control channel (PDCCH) andanother control channel are allocated to the control region, and aphysical downlink shared channel (PDSCH), and a physical broadcastchannel (PBCH) are allocated to the data region.

A physical control format indicator channel (PCFICH) transmitted in afirst OFDM symbol of the subframe carries a control format indicator(CFI) regarding the number of OFDM symbols (i.e., a size of the controlregion) used for transmission of control channels in the subframe. TheUE first receives the CFI on the PCFICH, and thereafter monitors thePDCCH. Unlike the PDCCH, the PCFICH does not use blind decoding, and istransmitted by using a fixed PCFICH resource of the subframe.

A physical hybrid-ARQ indicator channel (PHICH) which is transmittedfrom the control region, and carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink hybridautomatic repeat request (HARD). The ACK/NACK signal for UL data on aPUSCH transmitted by the UE is transmitted on the PHICH.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI may include resourceallocation of the PDSCH (this is referred to as a DL grant), resourceallocation of a PUSCH (this is referred to as a UL grant), a set oftransmit power control commands for individual UEs in any UE group,and/or activation of a voice over Internet protocol (VoIP).

The BS determines a PDCCH format according to DCI to be transmitted tothe UE, attaches a cyclic redundancy check (CRC) to the DCI, and masks aunique identifier (referred to as a radio network temporary identifier(RNTI)) to the CRC according to an owner or usage of the PDCCH.

If the PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI(C-RNTI)) of the UE may be masked to the CRC. Alternatively, if thePDCCH is for a paging message, a paging indication identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information, a system information identifier (e.g., systeminformation-RNTI (SI-RNTI)) may be masked to the CRC. To indicate arandom access response that is a response for transmission of a randomaccess preamble of the UE, a random access-RNTI (RA-RNTI) may be maskedto the CRC. When the C-RNTI is used, the PDCCH carries controlinformation for a specific UE (such information is called UE-specificcontrol information), and when another RNTI is used, the PDCCH carriescommon control information received by all or a plurality of UEs in acell.

The BS encodes the CRC-attached DCI to generate coded data. The encodingincludes channel encoding and rate matching. Thereafter, the BSmodulates the coded data to generate modulation symbols, and transmitsthe modulation symbols by mapping the symbols to a physical resourceelement (RE).

A PDSCH transmitted in the data region is a downlink data channel.System information, data, etc., can be transmitted through the PDSCH. Inaddition, the PBCH carries system information necessary forcommunication between the UE and the BS. The system informationtransmitted through the PBCH is referred to as a master informationblock (MIB). In comparison thereto, system information transmitted onthe PDCCH is referred to as a system information block (SIB).

FIG. 5 shows a structure of a UL subframe.

Referring to FIG. 5, the UL subframe can be divided into a controlregion and a data region. The control region is a region to which aphysical uplink control channel (PUCCH) carrying UL control informationis allocated. The data region is a region to which a physical uplinkshared channel (PUSCH) carrying user data is allocated.

The PUCCH is allocated in an RB pair in a subframe. RBs belonging to theRB pair occupy different subcarriers in each of a first slot and asecond slot.

FIG. 6 shows a frame structure for synchronization signal transmissionin the conventional FDD frame. A slot number and a subframe number startfrom 0.

Herein, a synchronization signal is a signal used when a cell search isperformed, and includes a primary synchronization signal (PSS) and asecondary synchronization signal (SSS).

The synchronization signal can be transmitted in each of subframes #0and #5 by considering a global system for mobile communication (GSM)frame length of 4.6 ms to facilitate inter-RAT measurement. A boundaryfor the frame can be detected through the SSS. More specifically, in theFDD system, the PSS is transmitted in a last OFDM symbol of 0^(th) and10^(th) slots, and the SSS is transmitted in an immediately previousOFDM symbol of the PSS. The synchronization signal can transmit 504physical cell IDs by combining 3 PSSs and 168 SSSs. A physical broadcastchannel (PBCH) is transmitted in first 4 OFDM symbols of a first slot.The synchronization signal and the PBCH are transmitted within 6 RBs ina system bandwidth, so as to be detected or decoded by a UE irrespectiveof a transmission bandwidth. A physical channel for transmitting the PSSis called a P-SCH, and a physical channel for transmitting the SSS iscalled an S-SCH.

A transmit diversity scheme of the synchronization signal uses only asingle antenna port, and is not separately defined in the standard. Thatis, single antenna transmission or UE-transparent transmission (e.g.,precoding vector switching (PVS), time switched transmit diversity(TSTD), cyclic delay diversity (CDD)) can be used.

For the PSS, a length-63 Zadoff-Chu (ZC) sequence is defined in afrequency domain and is used as a sequence of the PSS. The ZC sequenceis defined by Equation 1. A sequence element corresponding to a DCsubcarrier, i.e., n=31, is punctured. In Equation 1, Nzc=63.

$\begin{matrix}{{d_{u}(n)} = {\mathbb{e}}^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{N_{ZC}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Among 6 RBs (i.e., 72 subcarriers), 9 (=72−63) remaining subcarriers arealways transmitted with a value of ‘0’, which facilitates a filterdesign for performing synchronization. To define 3 PSSs, u=25, 29, and34 are used in Equation 1. In this case, since 29 and 34 have aconjugate symmetry relation, two correlations can be simultaneouslyperformed. Herein, the conjugate symmetry implies the relation ofEquation 2 below, and by using this characteristic, a one-shotcorrelator can be implemented for u=29, 34, and an overall computationamount can be decreased by about 33.3%.d _(u)(n)=(−1)^(n)(d _(N) _(ZC) _(-u)(n))*, when N _(ZC) is even number.d _(u)(n)=(d _(N) _(ZC) _(-u)(n))*, when N _(ZC) is oddnumber.  [Equation 2]

A sequence used for the SSS is used by interleaving two m-sequenceshaving a length of 31. The SSS can transmit 168 cell group IDs bycombining two sequences. An m-sequence used as a sequence of the SSS isrobust to a frequency selective environment, and can decrease acomputation amount according to a fast m-sequence transform using a fastHadamard transform. In addition, it is proposed to configure the SSS byusing two short codes in order to decrease a computation amount of theUE.

FIG. 7 shows a case where two sequences in a logical domain areinterleaved and mapped in a physical domain.

Referring to FIG. 7, when two m-sequences used to generate an SSS codeare respectively defined by S1 and S2, if an SSS of a subframe 0transmits a cell group ID by combining the two sequences (S1, S2), anSSS of a subframe 5 is transmitted by swapping to (S2, S1), therebybeing able to identify a boundary of 10 m frame. The SSS code usedherein uses a generator polynomial of x⁵+x²+1, and 31 codes can begenerated by using different circular shifts.

To improve reception performance, two different PSS-based sequences aredefined and then are scrambled to an SSS such that different sequencesare scheduled to S1 and S2. Thereafter, an S1-based scheduling code isdefined, and scheduling is performed on S2. In this case, a code of theSSS is swapped in a unit of 5 ms, whereas the PSS-based scrambling codeis not swapped. The PSS-based scrambling code can be defined as aversion of 6 circular shifts according to an index of PSS at anm-sequence generated from a generator polynomial of x⁵+x³+1. TheS1-based scrambling code can be defined as a version of 8 circularshifts according to an index of S1 at an m-sequence generated from agenerator polynomial of x⁵+x⁴+x³+x²+x¹+1.

FIG. 8 shows a frame structure for transmitting a synchronization signalin the conventional TDD frame.

In a TDD frame, a PSS is transmitted in a third OFDM symbol of third and13^(th) slots. An SSS is transmitted three OFDM symbols earlier than theOFDM symbol in which the PSS is transmitted. A PBCH is transmitted infirst 4 OFDM symbols of a second slot of a first subframe.

Now, a carrier aggregation system will be described.

FIG. 9 shows an example of comparing a single-carrier system and acarrier aggregation system.

Referring to FIG. 9, only one carrier is supported for a UE in an uplinkand a downlink in the single-carrier system. Although the carrier mayhave various bandwidths, only one carrier is assigned to the UE.Meanwhile, multiple component carriers (CCs) (i.e., DL CCs A to C and ULCCs A to C) can be assigned to the UE in the carrier aggregation (CA)system. For example, three 20 MHz CCs can be assigned to allocate a 60MHz bandwidth to the UE.

The carrier aggregation system can be divided into a contiguous carrieraggregation system in which carriers are contiguous to each other and anon-contiguous carrier aggregation system in which carriers areseparated from each other. Hereinafter, when it is simply called thecarrier aggregation system, it should be interpreted such that bothcases of contiguous CCs and non-contiguous CCs are included.

A CC which is a target when aggregating one or more CCs can directly usea bandwidth that is used in the legacy system in order to providebackward compatibility with the legacy system. For example, a 3GPP LTEsystem can support a carrier having a bandwidth of 1.4 MHz, 3 MHz, 5MHz, 10 MHz, 15 MHz, and 20 MHz, and a 3GPP LTE-A system can configure abroadband of 20 MHz or higher by using each carrier of the 3GPP LTEsystem as a CC. Alternatively, the broadband can be configured bydefining a new bandwidth without having to directly use the bandwidth ofthe legacy system.

A frequency band of a wireless communication system is divided into aplurality of carrier frequencies. Herein, the carrier frequency impliesa center frequency of a cell. Hereinafter, the cell may imply a downlinkfrequency resource and an uplink frequency resource. Alternatively, thecell may also imply combination of a downlink frequency resource and anoptional uplink frequency resource. In general, if carrier aggregation(CA) is not considered, uplink and downlink frequency resources canalways exist in pair in one cell.

In order to transmit and receive packet data through a specific cell,the UE first has to complete a configuration of the specific cell.Herein, the configuration implies a state of completely receiving systeminformation required for data transmission and reception for the cell.For example, the configuration may include an overall procedure thatrequires common physical layer parameters necessary for datatransmission and reception, media access control (MAC) layer parameters,or parameters necessary for a specific operation in a radio resourcecontrol (RRC) layer. A cell of which configuration is complete is in astate capable of immediately transmitting and receiving a packet uponreceiving only information indicating that packet data can betransmitted.

The cell in a state of completing its configuration can exist in anactivation or deactivation state. Herein, the activation implies thatdata transmission or reception is performed or is in a ready state. TheUE can monitor or receive a control channel (i.e., PDCCH) and a datachannel (i.e., PDSCH) of an activated cell in order to confirm aresource (e.g., frequency, time, etc.) allocated to the UE.

The deactivation implies that transmission or reception of traffic datais impossible and measurement or transmission/reception of minimuminformation is possible. The UE can receive system information (SI)required for packet reception from a deactivated cell. On the otherhand, the UE does not monitor or receive a control channel (i.e., PDCCH)and a data channel (i.e., PDSCH) of the deactivated cell in order toconfirm a resource (e.g., frequency, time, etc.) allocated to the UE.

A cell can be classified into a primary cell, a secondary cell, aserving cell, etc.

When carrier aggregation is configured, the UE has only one RRCconnection with the network. In an RRC connectionestablishment/re-establishment, handover process, one cell providesnon-access stratum (NAS) mobility information and a security input. Sucha cell is called a primary cell. In other words, the primary cellimplies one serving cell which provides a security input in an RRCconnection establishment procedure/connection re-establishmentprocedure/handover procedure performed by the UE with respect to the BS.

The secondary cell implies a cell configured to provide an additionalradio resource after establishing an RRC connection through the primarycell.

The serving cell is configured with the primary cell in case of a UE ofwhich carrier aggregation is not configured or which cannot provide thecarrier aggregation. If the carrier aggregation is configured, the term‘serving cell’ is used to indicate a cell configured for the UE, and thecell may be plural in number. A plurality of serving cells may beconfigured with a set consisting of a primary cell and one or aplurality of cells among all secondary cells.

A primary component carrier (PCC) denotes a CC corresponding to theprimary cell. The PCC is a CC that establishes an initial connection (orRRC connection) with the BS among several CCs. The PCC serves forconnection (or RRC connection) for signaling related to a plurality ofCCs, and is a CC that manages a UE context which is connectioninformation related to the UE. In addition, the PCC establishes aconnection with the UE, and thus always exists in an activation statewhen in an RRC connected mode. A downlink CC corresponding to theprimary cell is called a downlink primary component carrier (DL PCC),and an uplink CC corresponding to the primary cell is called an uplinkprimary component carrier (UL PCC).

A secondary component carrier (SCC) denotes a CC corresponding to asecondary cell. That is, the SCC is a CC allocated to the UE in additionto the PCC. The SCC is an extended carrier used by the UE for additionalresource allocation or the like in addition to the PCC, and can be in anactivation state or a deactivation state. A DL CC corresponding to thesecondary cell is called a DL secondary CC (SCC). A UL CC correspondingto the secondary cell is called a UL SCC.

The primary cell and the secondary cell have the following features froma perspective of each UE.

First, the primary cell is used for PUCCH transmission. Second, theprimary cell is always activated, whereas the secondary cell isactivated/deactivated according to a specific condition. Third, when theprimary cell experiences a radio link failure (RLF), RRCre-establishment is triggered. Fourth, the primary cell can change by ahandover procedure accompanied by a random access channel (RACH)procedure or security key modification. Fifth, non-access stratum (NAS)information is received through the primary cell. Sixth, in case of anFDD system, the primary cell always consists of a pair of a DL PCC and aUL PCC. Seventh, for each UE, a different CC can be configured as theprimary cell. Eighth, the primary cell can be replaced only through ahandover, cell selection/cell reselection process. When adding a newsecondary cell, RRC signaling can be used for transmission of systeminformation of a dedicated secondary cell.

Regarding a CC constituting a serving cell, a DL CC can construct oneserving cell. Further, the DL CC can be connected to a UL CC toconstruct one serving cell. However, the serving cell is not constructedonly with one UL CC.

Activation/deactivation of a CC is equivalent to the concept ofactivation/deactivation of a serving cell. For example, if it is assumedthat a serving cell 1 consists of a DL CC 1, activation of the servingcell 1 implies activation of the DL CC 1. If it is assumed that aserving cell 2 is configured by connecting a DL CC 2 and a UL CC 2,activation of the serving cell 2 implies activation of the DL CC 2 andthe UL CC 2. In this sense, each CC can correspond to a cell.

The number of CCs aggregated between a downlink and an uplink may bedetermined differently. Symmetric aggregation is when the number of DLCCs is equal to the number of UL CCs. Asymmetric aggregation is when thenumber of DL CCs is different from the number of UL CCs. In addition,the CCs may have different sizes (i.e., bandwidths). For example, if 5CCs are used to configure a 70 MHz band, it can be configured such as 5MHz CC(carrier #0)+20 MHz CC(carrier #1)+20 MHz CC(carrier #2)+20 MHzCC(carrier #3)+5 MHz CC(carrier #4).

As described above, the carrier aggregation system can support multiplecomponent carriers (CCs) unlike a single-carrier system.

The present invention will now be described.

In the carrier aggregation system, one UE may transmit and receivedata/control information using multiple cells. The UE uses a cell thatis initially connected as a primary cell, and uses the cell that isadditionally configured through the primary cell as a secondary cell.

As described above, the primary cell is used for the operation formaintaining the connection between a BS and a UE. For example, in theprimary cell may be performed the operations such as radio linkmanagement (RLM), radio resource management (RRM), reception of systeminformation, physical random access channel (PRACH) transmission, uplinkcontrol channel (PUCCH) transmission, and the like. Meanwhile, thesecondary cell is mainly used for the transmission of the schedulinginformation for data channels or the data channels.

The primary cell and the secondary cell are UE-specific. When multiplecells exist in a system, each of the cells may be used for the primarycell or the secondary cell, and each of the UEs uses one of the multiplecells as the primary cell. That is, an arbitrary cell may be used as theprimary cell or the secondary cell. Accordingly, all of the cells areconfigured to perform the operation of the primary cell.

In other words, all of the cells are expected to implement all of theseoperations such as the transmission of synchronization signal, thetransmission of broadcast channel, the transmission of CRS, theconfiguration of PDCCH region, and the like are implemented. Those cellsmay be referred to as backward compatible cells or legacy carrier type(LCT) in the aspect of carrier.

Meanwhile, if a cell is used as the secondary cell in the futurewireless communication system, it is considered to introduce the cell ofwhich a part or all of the unnecessary information is removed. Such acell may be represented not to have backward compatibility, and referredto as a new carrier type (NCT) or extension carrier in comparison withthe LCT.

For example, in the NCT, it may be configured to transmit the CRS onlyat a part of time interval or only at frequency interval withouttransmitting in every subframe, or the DL control channel region may benewly configured, which is specified for each UE by removing the DLcontrol channel region such as existing PDCCH or reducing to a timeregion or frequency region.

Such an NCT may be a carrier in which only DL transmission is allowed.Hereinafter, the carrier in which only DL transmission is allowed isshort for a DL only carrier, for the convenience.

FIG. 10 exemplifies the DL only carrier.

The DL only carrier may be configured by various methods. For example,in FDD, the DL only carrier may be a cell in which only DL CC exists.That is, as shown in FIG. 10(a), in FDD, the DL only carrier may be theDL CC in which corresponding UL CC does not exist. Or, even for the DLCC in which exists the UL CC that is linked by system information block(SIB), the DL only carrier may be configured by setting to use only DLCC without using the UL CC.

In TDD, the DL only carrier uses the UL-DL configuration of Table 1 andit is available to be generated to use the DL subframe only according tothe corresponding UL-DL configuration. In the LCT, UL subframe/DLsubframe are included by time division in a frame according to the UL-DLconfiguration defined in Table 1, but in the DL only carrier, only DLsubframe is included as shown in FIG. 10(b). However, such a methodcauses resource waste since the subframe which is supposed to beconfigured as UL subframe is not going to be used according to the UL-DLconfiguration.

Accordingly, in case that the DL only carrier is used in TDD, it ispreferable that all of the subframes in a frame are comprised of DLsubframes only.

For this, additional UL-DL configuration may be added in theconventional UL-DL configuration as shown in Table 1. The followingtable represents an example of UL-DL configuration according to thepresent invention.

TABLE 2 Uplink-downlink Downlink-to-Uplink subframe number configurationSwitch-point periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D 7 — D D D D D D D D D D

In Table 2, UL-DL configurations 0 to 6 are the same as those of theexisting UL-DL configuration, and the UL-DL configuration 7 is addedonto it. The UL-DL configuration 7 represents that all of the subframesin a frame are configured as DL subframe. It may be limited that UL-DLconfiguration 7 is used only for the secondary cell without being usedfor the primary cell. In other words, in order to avoid interferencebetween frequency bands, it may be limited that the DL only carrier useonly frequency band (the secondary cell) which is different from that ofthe existing TDD primary cell.

The method above may define the UL-DL configuration 7 in order toconfigure the DL only carrier and directly notify it to a UE.

FIG. 11 shows another example of configuring the DL only carrier.

Referring to FIG. 11, the BS transmits the UL-DL configuration andswitch information (S101).

The UL-DL configuration may be one of the existing UL-DL configurations0 to 6 of Table 1.

The switch information may be the information that represents UL whetherit is changed to the UL subframe in the corresponding UL-DLconfiguration, and whether it is changed to the DL subframe of a specialsubframe. According to the switch information, all of the UL subframes(or S subframe) in a frame may be switched to the DL subframe, or only apart of UL subframes (or S subframe) may be switched to DL subframe. Theswitch information may be implemented in various ways. For example, theswitch information represents whether the UL subframe (or S subframe)has been used or not, but what the UL subframe (or S subframe) has beennot used may mean that the UL subframe (or S subframe) is used as a DLsubframe.

For the configuration of the DL only carrier, it may be applied for themethod of stopping the use of the UL subframe (for example, onlysuspending the channel which is transmitted from the first SC-FDMAsymbol are transmitted in the UL subframe such as PUSCH, PUCCH, and soon but available to use the channel which is transmitted from the lastSC-FDMA symbol of the UL subframe such as SRS) or the method that theconfiguration of the UL subframe is changed to the DL subframe to use.

Herein, it is available to change the S subframe to the DL subframeowing to not using the UL subframe. In case of changing the S subframeonly to GP and the DL subframe that doesn't contain the UpPTS to usewithout switching the UL subframe to the DL subframe, there isadvantages that the unnecessary GP and UpPTS may be used in downlink andthe time relations of the control channel transmission of the DL/UL HARQprocess, data channel transmission, HARQ-ACK transmission and so on inthe existing UL-DL configuration may be applied same as the existingdefinition without any changes. Or, in case of utilizing the existingTDD UL-DL configuration not using the UL subframe while the DL subframeis left, it is available to designate to use the UL-DL configuration 5only which has the least UL subframes.

The UE, if the switch information is detected, switches the UL subframe(or the S subframe) of the UL-DL configuration to the DL subframe (step,S102). The switch information may transmit in the correspondingcell-specific signaling or UE-specific signaling.

If the DL only carrier use is used for the carrier aggregation, there isan advantage that the DL only carrier use above is shared as thesecondary cell between the FDD terminal and the TDD terminal in common.

The carrier that is configured only for DL use and available foraggregation is not limited to NCT but applied for LCT.

Meanwhile, the DL only carrier use may have two formats. That is, theFDD format and the TDD format are those. The DL only carrier useperformed by the FDD format (hereinafter the carrier only for FDD DL useis short for it) is the DL only carrier in which synchronization signal,PBCH, user-specific reference signal (URS) and so on are transmitted bythe FDD method (referring to FIG. 6). The DL only carrier use performedby the TDD format (hereinafter the carrier only for TDD DL use is shortfor it) is the DL only carrier in which synchronization signal, PBCH,URS and so on are transmitted by the TDD method (referring to FIG. 8).The URS may be a reference that is used for demodulation of thedata/control signal as a UE-specific reference signal. All of thecarriers only for DL use of two formats are common in that all of thesubframes within a frame are DL subframes, but different in thestructures of the synchronization signal, PBCH and so on.

In case that the secondary cell is added in the primary cell, theprimary cell may be the cell that is operated by TDD or FDD, and in casethat the secondary cell is the DL only carrier use, the DL only carrieruse above may be the carrier only for TDD DL use or the carrier only forFDD DL use. Therefore, four combinations are available in all.

When the base station configures the DL only carrier use as thesecondary cell in addition to the UE, it may notify whether theadditional DL only carrier use is the carrier only for TDD DL use or thecarrier only for FDD DL use. Or when the base station command themeasurement of a specific carrier to the UE, it may notify which one isit either the carrier only for TDD DL use and the carrier only for FDDDL use. Such information that is about the format of the carrier wave isreferred to as the frame structure indicating information. The framestructure indicating information makes it easy to detect the PSS/SSS ofthe secondary cell and the cell ID.

Or, without any overt signaling of the base station that is same as theframe structure indicating information, the UE may recognize the formatof the secondary cell through the process that the additional secondarycell detects the PSS/SSS.

In case of confirming the frame boundaries of the primary cell andsecondary cell, it is available to recognize the frame structure withonly the location of the PSS to be detected (that is, the subframenumber that the PSS is detected and the OFDM symbol). Accordingly, thebase station may transmit the frame structure indicating informationonly in case that the frame boundaries of the primary cell and thesecondary cell is not agreed, or transmit it to the UE only in case ofcommanding the measurement of the secondary cell. It may be applied tothe aggregation of the TDD primary cell and the FDD secondary cell andthe aggregation of the FDD primary cell and the TDD secondary cellidentically as well as the DL only carrier use.

Meanwhile, in case that the primary cell that is operated by the FDD(FDD primary cell) is aggregating the secondary cell that is operated bythe TDD (TDD secondary cell), the DL only carrier use may be applied forthe TDD secondary cell. In this case, there is a case that the DLsubframe which is a CSI detection object in the TDD secondary cell is tobe restricted as the DL subframe of the UL-DL configuration. This isbecause, even though corresponding UE does not use the UL subframe ofthe UL-DL configuration, the other UE may be configured to use thecorresponding UL subframe for the UL transmission.

In case that the primary cell that operates as the TDD (the TDD primarycell) aggregates the secondary cell that operates as the FDD (the FDDsecondary cell), the DL only carrier may be applied to the FDD secondarycell. In this case, the DL subframe which is an object for CSI detectionmay be restricted as the DL subframe of the UL-DL configuration. This isuseful, by applying the existing UL-DL configuration to the secondarycell and using only the corresponding DL subframe, that is, the casethat the secondary cell is used only for DL in the way that the ULsubframe of the corresponding UL-DL configuration is not used.

Or, the NCT may be the carrier in which UL transmission is only allowed.Hereinafter, the carrier in which only UL transmission is allowed isshort for a UL only carrier, for the convenience.

FIG. 12 exemplifies the UL only carrier.

The UL only carrier may be configured by various methods. For example,in FDD, the UL only carrier may be a cell in which only UL CC exists.That is, as shown in FIG. 12(a), in FDD, the UL only carrier may be theDL CC in which corresponding UL CC does not exist. Or, even for the ULCC in which exists the UL CC that is linked by system information block(SIB), the UL only carrier may be configured by setting to use only ULCC without using the DL CC.

In TDD, the UL only carrier uses the UL-DL configuration of Table 1 andit is available to be generated to use only UL subframe without usingthe DL subframe according to the corresponding UL-DL configuration. Inthe LCT, UL subframe/DL subframe are included by time division in aframe according to the UL-DL configuration defined in Table 1, but inthe UL only carrier, only UL subframe is included as shown in FIG.10(b). However, such a method causes resource waste since the subframe(for example, 101 and 102) which is supposed to be configured as DLsubframe is not going to be used according to the UL-DL configuration.

Accordingly, in case that the UL only carrier is used in TDD, it ispreferable that all of the subframes in a frame are comprised of ULsubframes only.

For this, additional UL-DL configuration may be added in theconventional UL-DL configuration as shown in Table 1. The followingtable represents an example of UL-DL configuration according to thepresent invention.

TABLE 3 Uplink-downlink Downlink-to-Uplink subframe number configurationSwitch-point periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D 7 — U U U U U U U U U U

In Table 3, UL-DL configurations 0 to 6 are the same as those of theexisting UL-DL configuration, and the UL-DL configuration 7 is addedonto it. The UL-DL configuration 7 represents that all of the subframesin a frame are configured as UL subframe. It may be limited that UL-DLconfiguration 7 is used only for the secondary cell without being usedfor the primary cell. In other words, in order to avoid interferencebetween frequency bands, the UL only carrier may be used for thesecondary cell in a different frequency band which is different fromthat of the existing TDD primary cell. The method above may define theUL-DL configuration 7 in order to configure the DL only carrier anddirectly notify it to a UE.

Meanwhile, a BS selects one of the DL only carrier and the UL onlycarrier and aggregates it as a secondary cell, UL-DL configuration 7 ofTable 2 may be added to Table 3. That is, total nine UL-DLconfigurations may be included in Table 3, and UL-DL configuration 7 ofTable 2 may be added to Table 3 as UL-DL configuration 8.

Or, a BS uses the existing UL-DL configurations 0 to 6 but mayadditionally use the method of transmitting information indicating theDL only carrier or the UL only carrier.

Hereinafter, in the DL only carrier, it is assumed that all subframes ina frame are comprised of DL subframes as shown in FIG. 10(a), and the DLHARQ-ACK (hereinafter, shortened by HARQ-ACK) timing will be describedin case that the DL only carrier is aggregated to a secondary cell.

The existing FDD has the HARQ-ACK timing when transmitting the ACK/NACKfor a data unit (for example, a transmission block, codeword, and etc.)that a UE receives in subframe n−4 by subframe n. In TDD has theHARQ-ACK timing as represented by following table. In Table 4, eachvalue may be represented by aggregation K, and has the element of K={k₀,k₁, . . . , k_(M-1)}. For example, in UL-DL configuration 1, K={7, 6}and M=2 for subframe 2. The terms k₀, k₁, . . . ,k_(M-1) may berepresented by k_(m)(m=0, 1, . . . , or M−1).

TABLE 4 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, 4, 11, 6 — — — — — — — 6 — — 7 7 5 — —7 7 —

Table 4 shown above represents the corresponding relation of the DLsubframe n-k_(m) that corresponds to UL subframe n in each UL-DLconfiguration as the value of k_(m). That is, it signifies that theACK/NACK for the PDSCH which is transmitted from subframe n-k_(m) istransmitted from UL subframe n.

However, in case of using the TDD DL only carrier for a secondary cell,the configuration of DL HARQ timing of the secondary cell may beproblematic. That is, the configuration of ACK/NACK response timingthrough the primary cell for the PDSCH which is received in thesecondary cell is required.

Method 1.

Method 1 is the method that the HARQ-ACK timing for a secondary cell isto follow the DL HARQ-ACK timing which is configured according to theUL-DL configuration which is configured in a primary cell. For example,in case that the primary cell is a TDD cell and uses UL-DL configuration1 and the secondary cell is the DL only carrier, the ACK/NACK for thedata unit which is received in subframe 0 of the secondary cell istransmitted from subframe 7 of the primary cell, in this time, subframe7 is a subframe configured to transmit ACK/NACK for the data unit whichis received in subframe 0 of the primary cell.

Method 2.

There is a configuration that the number of DL subframe is more thanthat of the UL subframe in a frame among the UL-DL configurations. Forexample, UL-DL configurations 2, 4, 5, and the like have more DLsubframes more than UL subframes. Like this, the DL HARQ-ACK timingaccording to the UL-DL configuration that has more DL subframes may beused as the HARK-ACK reference timing of a secondary cell. However, theUL subframes according to the UL-DL configuration of the secondary cellshould be subset of the UL subframes according to the UL-DLconfiguration of a primary cell.

For example, in case that the UL-DL configuration of the primary cell is0, 1 and 2, the HARQ-ACK timing according to UL-DL configuration 2 and 5may be used as the HARK-ACK reference timing of a secondary cell. Incase that the UL-DL configuration of the primary cell is 3, 4, 5 and 6,the HARQ-ACK timing according to UL-DL configuration 5 may be used asthe HARK-ACK reference timing of a secondary cell.

According to Method 1 and Method 2 above, a HARQ-ACK timing isdetermined for the DL subframe of the secondary cell which is overlappedwith the DL subframe of the primary cell. However, a HARQ-ACK timing isnot determined for the DL subframe of the secondary cell which isoverlapped with the UL subframe of the primary cell. The HARQ-ACK timingfor the DL subframe of the secondary cell which is overlapped with theUL subframe of the primary cell may use one of the following methods.That is, Methods 1 and 2 and Methods 3 to 7 may be used with beingcombined.

Method 3.

This is the method for selecting the subframe of the fastest primarycell that satisfies the minimum required time (for example, k_(m)=4)which is available to ACK/NACK after receiving a data unit in thesubframe of the secondary cell.

Method 4.

Method 4 is the method that the number of ACK/NACK transmitted from eachUL subframe is to be equally arranged in the multiple UL subframespreferably without being biased to a specific UL subframe by equalizingthe number of DL subframe of the secondary cell that corresponds to eachUL subframe of the primary cell preferably.

First of all, Method 4 selects the subframe of the fastest primary cellthat satisfies the minimum required time (for example, k_(m)=4) which isavailable to ACK/NACK after receiving a data unit in each subframe ofthe secondary cell. By setting the biggest value k_(m) which isdetermined in each subframe as a reference timing, the UL subframe ofthe primary cell which is to transmit ACK/NACK for the data unit whichis received in each subframe of the secondary cell is determined. As anexample, the maximum ACK/NACK bit that is available to be transmitted byone UL subframe is determined, and if it exceed the maximum ACK/NACKbit, the UL subframe which is to transmit the ACK/NACK that exceeds themaximum ACK/NACK bit may be changed to the next UL subframe or theprevious UL subframe. In this time, the UL subframe is changed such thatthe ACK/NACK for the forgoing PDSCH is not to be transmitted later thanthe ACK/NACK for the following PDSCH.

The maximum ACK/NACK bit may be changed according to the UL-DLconfiguration.

When equally distributing the UL subframe of the primary cell thattransmits ACK/NACK, the method of equally distributing with includingthe timing in the existing UL-DL configuration, or the method of equallydistributing with new timing, that is, the timing which is added in caseof using the secondary cell as the DL only carrier.

In case of performing equal distribution considering the timing of theexisting UL-DL configuration, HARQ-ACK timing is deducted as representedby following table. Table 5 may be added to Table 4.

TABLE 5 UL-DL Configuration Subframe n (Primary cell) 0 1 2 3 4 5 6 7 89 0 — — 5 5, 4 — — 5 5, 4 1 — — 5  5 — — — 5 5 — 2 — — 5 — — — — 5 — — 3— — 10 10 10 — — — — — 4 — — 10 10 — — — — — — 5 — — 10 — — — — — — — 6— — 8  6  6 — — 5 5 —

According to the method of equally distributing for only new timing, thefollowing Table 6 may be Table 4.

TABLE 6 UL-DL Configuration Subframe n (Primary cell) 0 1 2 3 4 5 6 7 89 0 — — 5 5 5 — — 5 5 5

FIG. 13 shows the HARQ-ACK timing in case that Method 1 and Method 4 arecombined.

Referring to FIG. 13, the primary cell is a TDD cell according to UL-DLconfiguration 1, and the secondary cell uses the DL only carrier. Inthis case, the secondary cell is comprised of only DL subframes. TheACK/NACK for the PDSCH (or transmission block) which is received in theDL subframe of the secondary cell follows the HARQ-ACK timing of theprimary cell.

For example, the ACK/NACK for the PDSCH which is received in the DLsubframe 141 of the secondary cell is identical to the ACK/NACKtransmission timing for the PDSCH which is received in the DL subframe142 of the primary cell that corresponds to the DL subframe 141, andaccordingly, transmitted from the UL subframe 143 of the primary cell.The solid arrow lines represent the ACK/NACK transmission of thesecondary cell according to the HARQ-ACK timing of the primary cell.

Meanwhile, the HARQ-ACK timing of the DL subframe of the secondary cellwhich is overlapped with the UL subframe of the primary cell is setaccording to Method 4, becomes the HARQ-ACK timing according to thebroken arrow lines in FIG. 13. For example, the ACK/NACK for the dataunit which is received in the subframe 144 is transmitted from the ULsubframe 143 which is located behind 4 subframes and the fastest. TheACK/NACK for the data unit which is received in the subframe 146 istransmitted from the UL subframe 143 which is located behind 4 subframesand the next UL subframe 147, not the fastest UL subframe 143. This isfor equal distribution. In this case, the maximum ACK/NACK bit which isavailable to be transmitted from one UL subframe may be 3 bits.

According to the method, there is an effect of dispersing load since thebit number of ACK/NACK that should be transmitted from one UL subframecan be equalized.

Method 5.

This is the method of limiting the PDSCH scheduling for a specific DLsubframe of the secondary cell. For example, the PDSCH scheduling forthe DL subframe of the secondary cell which is overlapped with the ULsubframe of the primary cell is to be limited.

Exceptionally, the PDSCH transmission that does not require ACK/NACKresponse from the DL subframe of the secondary cell may be allowed. Forexample, there may be SIB transmission which is transmitted to thePDSCH.

Method 5 is available to be configured even though the UL-DLconfiguration which is comprised of only DL subframes like UL-DLconfiguration 7 of Table 2 is not introduced. For example, the existingUL-DL configurations 0 to 6 are allocated to the DL only carrier, butall of the special subframes may be used as the same structure of theother DL subframe. This is because the configuration of DwPTS, GP andUwPTS are not required in the special subframe since the UL subframe isnot used. In this case, when aggregating the DL only carrier in thesecondary cell, the signaling notifying that it is the DL only carrierwith the UL-DL configuration information (0 to 6). For example, theinformation notifying whether the UL subframe is used in thecorresponding UL-DL configuration or the special subframe is to be usedas perfect DL subframe.

Method 6.

Method 6 is the method of signaling the relation between the DL subframewhere the PDSCH is transmitted in the secondary cell and the UL subframeof the primary cell where the corresponding ACK/NACK is transmitted byradio resource control (RRC). Method 6 may be applied to overall DLsubframes of the secondary cell as well as to the DL subframe of thesecondary cell which is overlapped with the UL subframe of the primarycell, also may be commonly or partly applied to the case of aggregatingcarriers having different UL-DL configurations.

Method 7.

This is the method of transmitting all ACK/NACK in subframe 2 of theprimary cell in case that UL-DL configuration 5 is used among UL-DLconfigurations 0 to 6 as the reference configuration for the HARQ-ACKtiming of the secondary cell.

This is to limit the subframe of the primary cell that transmits theACK/NACK for the data unit which is received in the secondary cell to bethe subframe which is the common UL subframe for all UL-DLconfigurations. For example, referring to UL-DL configuration 0 to 6,subframe 2 is UL subframe for all UL-DL configurations.

Subframe 2 which is fixed to UL subframe for all UL-DL configurations inMethod 3 to 6 may be excluded in the timing configuration for PDSCHtransmission.

Meanwhile, when the reference UL-DL configuration for HARQ-ACK timing isapplied to the secondary cell in TDD, the set K_(Scell) in the referenceUL-DL configuration may be different from the set K_(Pcell) in the UL-DLconfiguration of the primary cell.

In this time, if the cross carrier scheduling in which the schedulinginformation and the PDSCH following the scheduling are transmitted indifferent carriers, the primary cell may schedule the secondary cell.The HARQ-ACK timing of the secondary cell is applied according to theset K_(Scell), for the element of K_(Scell) (k^(Scell) _(n)) having thesame value as the element of K_(Pcell) (k^(Pcell) _(n)) in the ULsubframe which is the same for the primary cell and the secondary cell,m of k^(Pcell) _(n) is applied when mapping implicit PUCCH resource ofthe primary cell (for example, in case of default antenna port,n^((1,p)) _(PUCCH)=(M m−1)·N_(c)+m·N_(c+1)+n_(CCE,m)+N⁽¹⁾ _(PUCCH)).

As an example, in case that the primary cell uses UL-DL configuration 2and the reference UL-DL configuration of the secondary cell is UL-DLconfiguration 1, k^(Scell) ₀=7, k^(Pcell) ₁=7 in the subframe 2 andconsequently m=1 is applied.

For the element k_(m) in the set K of Table 4, k_(m) denoting a specialsubframe in which the possibility of DL scheduling is low and DLscheduling may be restricted (for example, k_(m)=11 and 6 in set K thatcorresponds to subframe 2 or 7 in UL-DL configurations 3, 4 and 5 ork_(m)=7 in set K that corresponds to subframe 3) is exceptionallyarranged as the last element of K. This is for the unification withother UL-DL configurations.

This is to upgrade the efficiency of the use of the implied PUCCHresource that is corresponding to subframe n-k_(m) (that is, PUCCHformat 1a/1b resource that is corresponding to CCE occupied by PDCCH),it may avoid the collision of a region with the center part that is usedfor PUSCH by mapping the PUCCH resources from the both ends of thesystem bandwidth in consecutive order.

Therefore, the following method may be applied for the selection of thePUCCH resource corresponding to k_(m)′ value that is used to be addedwith the existing K_(Pcell) (for example, the value shown in Table 5).

Method 8.

Method 8 is a method that configures K′ separated from the existingK_(Pcell) and in case of the PUCCH format 1 a/1 b corresponding to theDL subframe n-k_(m)′ that is indicated by k_(m)′ of the newly added K′,it suggests to use the explicit PUCCH resource (the resource that isdirectly indicated by RRC, it is available to choose one among aplurality of RRC resources as ARI in addition) not to use the impliedPUCCH resource. That is, without any changes in the existing M_(Pcell)value, a separated K′ is added. This method is enabled to support a newHARQ-ACK timing without any changes in the rules of implied resourcesthat are conventionally used.

Meanwhile, in case that the UL-DL configuration is 0, two HARQ-ACKtimings might be occurred in a UL subframe. However such a method mightbe inefficient in the utility of the PUCCH resource. Accordingly, such amethod is considered that only one explicit PUCCH resource is allocatedand only one DL subframe among corresponding two DL subframes isscheduled.

Method 9.

Method 9 is a method that configures the implies mapping to becorresponded from the next of the implies PUCCH resource (towards thecenter of the bandwidth) to which the existing set K_(Pcell) iscorresponding in case of the PUCCH format 1a/1b corresponding to the DLsubframe n-k_(m)′ that is indicated by k_(m)′ of the newly added K′, byconfiguring K′ separated from the existing K_(Pcell). That is, it may beset up the correspondence of m value after existing value. This methoddoes not cause any changes in the existing MP_(Pcell) value either.

Method 10.

This is a method that is to correspond the mapping of the implies PUCCHresource which corresponds to a special subframe in the existing set Kin case of the PUCCH format 1a/1b corresponding to the DL subframen-k_(m)′ that is indicated by k_(m)′ of the newly added K′, byconfiguring K′ separated from the existing K_(Pcell). This is availableto share the corresponding resource as the scheduling for the specialsubframe is not quite often. This method does not cause any changes inthe existing M_(Pcell) value either.

Method 9 and 10 may be selectively applied on the circumstances. Forexample, method 9 may be applied in case that the special subframe isused for the DL subframe scheduling and otherwise, method 10 may beapplied.

Meanwhile, channel selection may be used for the ACK/NACK transmission.The channel selection is to select a PUCCH resource after allocating aplurality of PUCCH resources and to transmit a modulation symbol in theselected PUCCH resources. The detailed contents of ACK/NACK areclassified by the selected PUCCH resources and modulation symbol. Thechannel selection is enabled to transmit maximum 4 ACK/NACK bits.

In case that the channel selection is used, and the number (M) of the DLsubframe which corresponds to a UL subframe that transmits the ACK/NACKis bigger than 4, a part or the whole of the DL subframes of thesecondary cell that is overlapped with the UL subframe of the primarycell may be restricted on scheduling. In case of restricting a part, therelevant information may be signaled, and indirect information may beutilized such as the method for restricting the subframe set up as analmost blank subframe (ABS) considering the inter-cell interferencecoordination (ICIC). Or the order may be decided according to thepredetermined rule (for example, according to the order in which theACK/NACK response time is long or short).

The present invention illustrate the case that data unit is scheduled byPDCCH, but also may be applied to the case that it is scheduled byenhanced-PDCCH (E-PDCCH). The enhanced-PDCCH (E-PDCCH) is a controlchannel that is transmitted to the UE within the conventional PDSCHregion apart from the PDCCH. The E-PDCCH may be a control channel thatis decoded by URS not by CRS.

Meanwhile, in case that DL only carrier or UL only carrier areaggregated to the secondary cell in the primary cell that is operated byTDD or FDD, the DL only carrier or the UL only carrier may be DL carrieror UL carrier that is selected in the cell defined as a pair of ULcarrier and DL carrier.

The base station notifies the cell ID of the cell that is defined as thepair of UL carrier and DL carrier to the UE, and may signal theinformation to the UE whether the both UL carrier and DL carrier areaggregated at the same time or either one is aggregated in the cell thatis defined as the pair of the UL carrier and the DL carrier. The aboveinformation may be comprised of two-bit bitmap, and each bit of thebitmap may correspond to each UL carrier and DL carrier of the cell thatis defined as a pair of the UL carrier and DL carrier. According to eachbit value, it is available to inform which one is aggregated to thesecondary cell of the UL carrier and the DL carrier.

The information may be performed dynamically with L2/L1 signaling. As anexample of the L2 signaling, it is available to directly indicate theMAC message that is including the information that indicates the DLcarrier and the UL carrier. Or for example of an indirect method, it isalso available to notify activation/non-activation that are applied toDL carrier/UL carrier in common by existing cell unit with separating byDL carrier/UL carrier.

As for L1 signaling, it is available to notify by using an exclusivecontrol channel that sets up carrier or DL/UL scheduling controlchannel. In case of using the DL/UL scheduling control channel, it maybe set up to ignore the DL/UL scheduling.

Additionally, in case that DL only carrier or UL only carrier areaggregated in the primary cell that is operated in TDD or FDD, bynotifying the cell ID of the cell defined for TDD (that is, the cellthat is configured with the carrier having the mixture of DL/ULsubframes) and the cell that corresponds to the cell ID above may beaggregated to the secondary cell.

FIG. 14 is a block diagram illustrating a wireless device in which anembodiment of the present invention is implemented.

ABS 100 includes a processor 110, a memory 120, and a radio frequency(RF) unit 130. The processor 110 implements the proposed functions,procedures, and/or methods. For example, the processor 110 transmitssynchronization signal configuration information for a secondary cellthrough a primary cell, and transmits a synchronization signal throughthe secondary cell. A PBCH can be transmitted in the secondary cell. Thememory 120 is coupled to the processor 110, and stores a variety ofinformation for driving the processor 110. The RF unit 130 is coupled tothe processor 110, and transmits and/or receives a radio signal.

A UE 200 includes a processor 210, a memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, procedures, and/ormethods. For example, the processor 210 may configure the DL onlycarrier as the secondary cell using the UL-DL configuration and/orswitch information. The ACK/NACK for the data unit which is receivedthrough the secondary cell is transmitted through the primary cell, andits HARQ-ACK timing and resource may be referred to the above describedmethods 1 to 9. The memory 220 is coupled to the processor 210, andstores a variety of information for driving the processor 210. The RFunit 230 is coupled to the processor 210, and transmits and/or receivesa radio signal.

The processors 110 and 210 may include an application-specificintegrated circuit (ASIC), a separate chipset, a logic circuit, a dataprocessing unit, and/or a converter for mutually converting a basebandsignal and a radio signal. The memories 120 and 220 may include aread-only memory (ROM), a random access memory (RAM), a flash memory, amemory card, a storage medium, and/or other equivalent storage devices.The RF units 130 and 230 may include one or more antennas fortransmitting and/or receiving a radio signal. When the embodiment of thepresent invention is implemented in software, the aforementioned methodscan be implemented with a module (i.e., process, function, etc.) forperforming the aforementioned functions. The module may be stored in thememories 120 and 220 and may be performed by the processors 110 and 210.The memories 120 and 220 may be located inside or outside the processors110 and 210, and may be coupled to the processors 110 and 210 by usingvarious well-known means.

What is claimed is:
 1. A method for transmitting an ACK/NACK(acknowledgement/not-acknowledgement) in a carrier aggregation system inwhich a primary cell and a secondary cell are aggregated, the methodperformed by a user equipment and comprising: receiving data in asubframe n-k of the secondary cell; and transmitting an ACK/NACK signalfor the data in a subframe n of the primary cell, wherein the primarycell uses a time division duplex (TDD) frame in which uplink subframesand downlink subframes are located at different times in the TDD frame,wherein the secondary cell uses a frequency division duplex(FDD) framein which uplink subframes and downlink subframes are located on twodifferent frequencies, respectively, and wherein when a UL-DLconfiguration for the primary cell is one of UL-DL configurationsincluded in the table below, wherein D denotes a downlink subframe, Sdenotes a special subframe and U denotes an uplink subframe: UL-DLSubframe number configuration 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U2 D S U D D D S U D D 5 D S U D D D D D D D

the subframe n and the subframe k are configured according to the tablebelow: UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6, 5 5,4 4 — — 6, 5 5, 4 4 2 — — 8, 7, 6, — — — — 8, 7, 6, — — 5, 4 5, 4 5 — —13, 12, 11, — — — — — — — 10, 9, 8, 7, 6, 5,
 4.


2. The method of claim 1, further comprising: receiving anuplink-downlink (UL-DL) configuration for the primary cell, wherein theUL-DL configuration indicates for each subframe included in the TDDframe whether it is a downlink subframe, a special subframe or an uplinksubframe, and wherein a UL-DL configuration for the secondary cell isdetermined based on the UL-DL configuration for the primary cell.
 3. Themethod of claim 1, wherein the primary cell is a cell that performs aninitial connection establishment process or a connection reestablishmentprocess with a base station.
 4. An apparatus for transmitting anACK/NACK (acknowledgement/not-acknowledgement) in a carrier aggregationsystem in which a primary cell and a secondary cell are aggregated, theapparatus comprising: a radio frequency (RF) unit that transmits andreceives a radio signal; and a processor operationally connected withthe RF unit, wherein the processor receives data in a subframe n-k ofthe secondary cell, and transmits an ACK/NACK signal for the data in asubframe n of the primary cell, wherein the primary cell uses a timedivision duplex (TDD) frame in which uplink subframes and downlinksubframes are located at different times in the TDD frame, wherein thesecondary cell uses a frequency division duplex(FDD) frame in whichuplink subframes and downlink subframes are loacted on two differentfrequencies, respectively, and wherein when a UL-DL configuration forthe primary cell is one of UL-DL configurations included in the tablebelow, wherein D denotes a downlink subframe, S denotes a specialsubframe and U denotes an uplink subframe: UL-DL Subframe numberconfiguration 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U 2 D S U D D D SU D D 5 D S U D D D D D D D

the subframe n and the subframe k are configured according to the tablebelow: UL-DL Config- Subframe n uration 0 1 2 3 4 5 6 7 8 9 0 — — 6, 55, 4 4 — — 6, 5 5, 4 4 2 — — 8, 7, 6, 5, 4 — — — — 8, 7, 6, 5, 4 — — 5 —— 13, 12, 11, 10, — — — — — —  —. 9, 8, 7, 6, 5, 4


5. The apparatus of claim 4, wherein the processor is further receivesuplink-downlink (UL-DL) configuration for the primary cell, wherein theUL-DL configuration indicates for each subframe included in the TDDframe whether it is a downlink subframe, a special subframe or an uplinksubframe and wherein an UL-DL configuration for the secondary cell isdetermined based on the UL-DL configuration for the primary cell.
 6. Theapparatus of claim 4, wherein a UL-DL configuration for the primary cellis one of the UL-DL configurations included in the table below: UL-DLSubframe number configuration 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U1 D S U U D D S U U D 2 D S U D D D S U D D 3 D S U U U D D D D D 4 D SU U D D D D D D 5 D S U D D D D D D D 6 D S U U U D S U U D.


7. The apparatus of claim 4, wherein the primary cell is a cell thatperforms initial connection establishment process or connectionreestablishment process with a base station.
 8. The method of claim 1,wherein a UL-DL configuration for the primary cell is one of the UL-DLconfigurations included in the table below: UL-DL Subframe numberconfiguration 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U 1 D S U U D D SU U D 2 D S U D D D S U D D 3 D S U U U D D D D D 4 D S U U D D D D D D5 D S U D D D D D D D 6 D S U U U D S U U D.